69 psi key on, engine off fuel pressure?!?

So I'm finally getting around to properly adjusting the fuel pressure on my suposedly '89 5.0 (turned out to be an 86 - flat top pistons, E6 heads with 89 computer and wiring, 19 lb injectors and unknown sensors). It's a very mismatched engine...

So anyway, I connected a tester under the hood and set it to about 38 psi but it ran crappy (had a hesitation) and my air fuel ratio guage read at the very bottom of LEAN. So I cranked it up til, at idle and warm, it sat at on the very bottom 2 stoich LED's which ended up being around 69 psi (when tested engine off, key on)! I know this is way high for a stock engine, but what can I do? Can't run it lean, but shouldn't run such high pressure. Anyone got any tips for me? Thanks!

I gotcha. It's just a digital Autometer.

I actually rechecked it and it was more like 60 psi.

But anyway, I took it out on the highway, and after about 5 minutes of 65 mph, it was up at 2-3 (of about 8) into RICH. So I dropped it down to about 58 and I'm gonna test that out and get it to a shop when I have a chance. But just out of curiousity, is there something that would cause my engine to need a higher pressure to run properly (maybe because of the mismathced parts and sensors)?

Also, how does a wideband gauge work?

Kam?

And what is stock FP?